R語(yǔ)言之正則表達(dá)式

正則表達(dá)式表通常被用來(lái)檢索、替換那些符合某個(gè)模式(規(guī)則)的文本。在我看來(lái)，正則表達(dá)式的主要用途有兩種：①查找特定的信息②查找并編輯特定的信息，也就是我們經(jīng)常用的替換。。比如我們要在Word，記事本等里面使用快捷鍵Ctrl+F，進(jìn)行查找一個(gè)特定的字符，或者替換一個(gè)字符，這就使用了正則表達(dá)式。

正則表達(dá)式的功能非常強(qiáng)大，尤其是在文本數(shù)據(jù)進(jìn)行處理中顯得更加突出。R中的grep、grepl、sub、gsub、regexpr、gregexpr等函數(shù)都使用正則表達(dá)式的規(guī)則進(jìn)行匹配。這幾個(gè)函數(shù)原型如下：

grep(pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE,

fixed = FALSE, useBytes = FALSE, invert = FALSE)

grepl(pattern, x, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

sub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

gsub(pattern, replacement, x, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

regexpr(pattern, text, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

gregexpr(pattern, text, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

regexec(pattern, text, ignore.case = FALSE, perl = FALSE,

fixed = FALSE, useBytes = FALSE)

這里是對(duì)參數(shù)進(jìn)行一個(gè)解釋說(shuō)明。

接下來(lái)我們對(duì)這幾個(gè)函數(shù)談?wù)勊麄兊牟煌c(diǎn)。

現(xiàn)在來(lái)舉幾個(gè)例子。

首先使用[]中括號(hào)的功能，來(lái)查找一下看有沒(méi)有do組合的單詞。

text<-c("Don't","aim","for","success","if","you","want","it","just","do","what","you","love",

"and","believe","in","and","it","will","come","naturally")

#查找含有DO組合的單詞

grep("[Dd]o",text)#不區(qū)分大小寫(xiě)

grep("[D]o",text)#D要大寫(xiě)

grep("[d]o",text)#D小寫(xiě)

運(yùn)行結(jié)果如下：

> text<-c("Don't","aim","for","success","if","you","want","it","just","do","what",

"you","love","and","believe","in","and","it","will","come","naturally")

> 數(shù)據(jù)分析培訓(xùn)

> #查找含有DO組合的單詞

> grep("[Dd]o",text)#不區(qū)分大小寫(xiě)

[1]  1 10

> grep("[D]o",text)#D要大寫(xiě)

[1] 1

> grep("[d]o",text)#D小寫(xiě)

[1] 10 

郵箱匹配：

#郵箱匹配：

text2<-c("704232753@qq.com is my email address.")

grepl("[0-9.*]+@[a-z.*].[a-z.*]",text2)

結(jié)果如下

> text2<-c("704232753@qq.com is my email address.")

> grepl("[0-9.*]+@[a-z.*].[a-z.*]",text2)

[1] TRUE

說(shuō)明可以查找到了。